The present invention relates to a method and a voltage source for producing a constant voltage "U" largely free of harmonics or ripples from three-phase current by using smoothing devices and relates in particular to high voltage power supplied for electron beam sources.
A pulsating direct current whose ripple can be reduced by smoothing devices, such as for example capacitors, can be produced from three-phase current be rectification. In the case of electron beam guns which are used for material processing and treatment such as welding, boring, milling, melting and vaporization, the size and position of the so-called focal spot on the material to be processed must be maintained as accurately as possible. By the term "focal spot" is meant that part of the material surface that is struck by the electron beam. The cross-section of the focal spot accordingly corresponds to the beam cross-section which, on account of the laws of electron optics image formation, is proportional to the projection of the beam source (cathode). In electron gun beams it is, above all, the quality of the high voltage power supply that determines the quality of the focal spot. In this connection, by the term "quality of the high voltage power supply" is meant its harmonic nature or ripple and its settling rate when subjected to disturbances, high quality meaning low ripple and rapid settling rate. This quality can be improved either by using electron tubes on the high voltage side or by using transistors in various circuits on the primary side of the high voltage power transformer. Electron tubes can be used only to a limited extent, however, on account of their high-voltage dielectric strength, heat production and service life. The use of transistors is restricted on account of their load limitation.